The invention relates to a method for examining the imaging behavior of first imaging optics, wherein an object is imaged into an image plane by second imaging optics and light in the image plane is detected in pixels in a spatially resolved manner, wherein the first and second imaging optics differ in at least one imaging characteristic, wherein values for the intensity as a first characteristic of the light and for at least one further, second characteristic of the light are determined for each pixel and stored in pixels, and the stored values are processed in an emulation step and an emulation image is generated, which emulates an image of the object generated by the first imaging optics, taking into consideration the imaging characteristic and the influence of the second characteristic on the imaging behavior.
The invention also relates to an apparatus for examining the imaging behavior of first imaging optics. Such an apparatus comprises second imaging optics, by which an object is imaged into an image plane and which differ from the first imaging optics in at least one imaging characteristic; a spatially resolving detector with pixels, by which the light in the image plane is detected in the pixels; a memory module in which values for intensity, as a first characteristic of the light, and for at least one further, second characteristic of the light are stored in a spatially resolved manner in pixels; as well as an emulation module, in which the stored values are processed and an emulation image is generated, which emulates an object image generated by the first imaging optics, taking into consideration the imaging characteristic and the influence of the second characteristic on the imaging behavior. The invention relates to the problem that dependencies on the second characteristic—which may be, for example, color or polarization—can be taken into consideration in the prior art only incompletely, e.g. summarily, in an emulation.
During emulation of the imaging characteristics of optical systems, inaccuracies may appear in the emulation. Some errors become particularly evident, for example, when high-aperture imaging optics are emulated by low-aperture imaging optics. For example, polarizing elements, such as polarizers or gratings, have been examined and evaluated so far substantially with respect to their integral effect. However, with the development of micro- or nano-structured optical components, the determination of local optical characteristics is gaining more and more importance for the further development and improvement of manufacturing processes and for the assurance of product quality. As an example of such optical components, a diffractive optical element (DOE) of the type used, for example, in the hybrid objective described in WO 03/001272 A3 should be mentioned here. The optical effect of this DOE occurs at the webs which are concentrically arranged around the optical axis. In this case, the distance between two webs is not constant, but varies depending on the radius. The purpose of this element is a dispersively imaging color compensation within the objective, in which case the optical quality of the objective results from the cooperation between the refractive lenses and the DOE. In order to avoid not being able to judge the optical characteristics of the DOE until the final assembly of the objective, it is desirable to study the optical effect previously in detail. This can be effected independently of the objective, or by insertion into the beam path of imaging optics, e.g. an emulation imaging system as second imaging optics for emulation of the respective objective, the first imaging optics. The insertion of the DOE usually requires an adaptation of the beam path, because both imaging optics differ at least in that respect. Moreover, the second imaging optics may also be designed to image the object such that it is magnified or reduced in size with respect to the objective.
Other examples of such components are classic linear diffraction gratings. In the case of gratings used in telecommunications, for example, an increasing number of line pairs per unit of surface area leads to an increase in the energy proportion and, thus, in the efficiency in the zeroth order of diffraction. The polarizing effect in the grating increases with an increasing number of lines, i.e. smaller structural dimensions.
Polarization effects also play a more and more important role in photolithographic scanners in which there is a trend towards increasingly larger numerical apertures and increasingly smaller mask structures. However, the emulation imaging methods and systems known so far in the prior art allow only an incomplete description of such polarization effects, because the polarization effect is taken into consideration only summarily, i.e. integrated via the image area.